The present invention relates to a device and a method for ignition of an internal combustion engine.
European Published Patent Application No. 0 344 394 describes a device and a method for ignition of an internal combustion engine. The device includes a circuit analyzing the primary voltage characteristic of an ignition coil as a function of time, but also requires an additional component. By comparison with a reference primary voltage characteristic, it is possible to detect when the primary voltage amplitude drops below a defined amplitude before a defined period of time has elapsed. This case is interpreted as misfiring.
German Published Patent Application No. 41 40 147 describes the characteristic of the secondary voltage or the operating voltage transformed to the primary side is detected by a sensor, and when ignition is correct, the signal applied to a diagnostic line is switched from 1 to 0 (or alternatively from 0 to 1). Cylinder-selective detection of faulty ignition is thus possible.
European Published Patent Application No. 0 020 069 describes a device in which the primary voltage characteristic is monitored so that the time difference during which the primary voltage exceeds a certain selected value is compared with a selected time difference. Misfiring is detected if the primary voltage remains above the given level for a time difference which is greater than the selected time difference.
The device and the method according to the present invention may provide the advantage that the characteristics of variables of the primary or secondary circuit are monitored by using threshold values. If values exceed or drop below the selected threshold values, a digital diagnostic line generates a signal edge which is analyzed in a microprocessor. The signal edges relayed via the diagnostic line permit an analysis of periods of time during which certain ignition states prevail. Given a suitable selection of threshold values, this analysis allows differentiation between various causes of misfiring, which thus makes it easier to identify and eliminate these causes. Another advantage is that the implementation of the device according to the present invention in terms of circuitry may require no additional component for ignition diagnosis.
The diagnostic signals of several variables such as the primary current and primary voltage as well as the diagnostic signals of several cylinders may be carried over one diagnostic bus line, taking into account the chronological order, and linked via a logic operations block or an open-collector circuit.
The time counter unit and a part of the arithmetic unit of the microprocessor may be accommodated in a time processing unit, which is arranged separately from the microcomputer and is coupled to it. Comparisons of signals with a continuous timer performed by the time processing unit do not thereby burden the capacity of the microcomputer.
It may be advantageous to investigate whether the measured periods of time are within setpoint intervals, because the operating parameters of the internal combustion engine are subject to certain fluctuations which allow the setpoint values to fluctuate within certain limits even with correct ignition. The limits of the setpoint intervals may be determined on the basis of model assumptions as a function of operating parameters of the internal combustion engine and to store them in the memory unit of the microcomputer. This storage may also take place during the application. The setpoint intervals are then read out of the memory unit for the respective comparison to be performed as a function of the corresponding operating parameters of the internal combustion engine. The battery voltage may be selected as an operating parameter. Another advantageous improvement may be achieved by determining the respective setpoint intervals on the basis of the measured time difference values by using statistical methods during the operation of the internal combustion engine. For certain applications, it may be advantageous to compare the measured time difference with a setpoint value. It may be advantageous to form a ratio of the measured time difference to the corresponding time difference of the preceding combustion cycle in the same cylinder. The ratio is then checked for a deviation from a ratio of 1. Fluctuations in temperature and battery voltage have hardly any effect on this ratio due to the small time interval between two combustion cycles. When analyzing the times, it may be possible to differentiate the cylinder-specific times on the basis of the activation signals, and thus a cylinder-specific fault analysis may be performed. The fault may be subsequently stored in the memory unit of the microcomputer with a reference to the respective cylinder, or output on a display unit, or cylinder-specific emergency measures may be taken.
When a certain selected first threshold value of a primary current is exceeded, a first signal edge, known as the first charging signal edge, may be generated in the respective diagnostic line, and in the case of a shutoff signal edge in the activation signal, a second signal edge, known as the second charging signal edge, may be generated in the respective diagnostic line.
In addition, it may also be advantageous to generate a second signal edge, the second excess temperature shutdown (xc3x9cFTA) signal edge, in the respective diagnostic line when an excess temperature shutdown of the controllable switch is detected. This yields the possibility of determining the starting time as a time difference between an activation edge in the activation signal of the respective cylinder and the first charging signal edge and to check on whether the starting time is within a first setpoint interval. Given a suitable choice of the first threshold value, it is possible to determine whether there is a short circuit to the battery voltage or a turn-to-turn fault in the ignition coil. The time between the first charging signal edge and the second charging signal edge may be determined as the-charging time, and a check may be performed to determine whether the charging time is within a second setpoint interval. It is possible to determine from this whether there is a loose contact in the peripheral unit or a fault in the microcomputer or the time processing unit. When a second excess temperature shutoff signal edge occurs before the second charging signal edge, the time difference between the first charging signal edge and the second excess temperature shutoff signal edge may be interpreted as charging time. Thus, it may also be possible to detect the occurrence of an excess temperature shutdown over the diagnostic line.
It may also be advantageous to generate a first signal edge, the first voltage signal edge, in the diagnostic line when the primary voltage exceeds a second threshold value and to generate a second signal edge, the second voltage signal edge, when the primary voltage falls below a third threshold value.
It may be advantageous to determine a rise time from the time difference between the shutoff signal edge of the activation signal and the first voltage signal edge. A rise time may be determined from the time difference between the shutoff signal edge of the activation signal and the first voltage signal edge, and an ignition time may be determined from the first voltage signal edge and the second voltage signal edge, in which case ignition may be interpreted as not having occurred if the rise time thus determined falls below a third setpoint value and if the ignition time exceeds a fourth setpoint value.